1. Field of the Invention
The invention relates in general to a clutch that produces a drive is connection between components when their relative rotation is in one direction, and overruns when relative rotation is in the opposite direction. In particular, the invention pertains to such clutches having rockers that engage or disengage at least partially due to the effect of centrifugal force acting on the rocker.
2. Description of the Prior Art
Conventional one-way clutches and brakes for producing a one-way drive connection between inner and outer races of the assembly include sprags or rollers for releasably driveably connecting the races and the components of a mechanical assembly connected to the races. One-way clutches and brakes perform satisfactorily in many cases, but certain applications, such as those in which a large magnitude of torque is transmitted by the component or those that provide only a small space for the component, require an unconventional sprag-type or roller-type clutch or brake to meet desire requirements.
Conventional one-way brakes and clutches have at least one sprag or roller, which driveably locks two notched or pocketed races together mutually in one rotary direction and allows the races to rotate freely in the other direction. Rocker and sprag type one-way brake assemblies can increase the torque capacity for a given package size compared to those of a roller-type brake, but they are generally limited in torque transmitting capacity by the magnitude of the contact or bearing stresses caused by contact of the rockers or sprags with the races.
To overcome these and other difficulties, a one-way overrunning clutch described in U.S. Pat. No. 5,070,978 includes a drive member and a driven member, which are mounted for clockwise and counterclockwise rotation about a common axis. The drive member includes a planar drive face, normal to the common axis, which connects with a source of power for rotating the planar drive face either clockwise or counterclockwise. The driven member includes a planar driven face, positioned in close proximity to and in confronting relationship with the drive face. The drive and driven members are coupled to one another through a series of pockets in one of the drive faces, and a plurality of cooperating struts carried by the other face, such that when the drive member is driven counterclockwise, it drives the driven member with it. When the drive member is driven clockwise, it does not drive the driven member, but rotates freely relative to the driven member. Column stability of the strut, which transmits the torsion load between the races, is an important factor in the design.
U.S. Pat. No. 5,954,174 discloses a ratchet one-way clutch assembly having an inner race with notches, an outer race with pockets, and rockers located in the pockets to engage the notches. The rockers have a pivot ridge which mates with a peak or recess in the pockets in the outer race to position the rocker in the pocket. The center of mass of each rocker is located such that the rocker tends to engage or disengage a notch in the inner race. A spring is used to provide a tilting force on each rocker directed to produce engagement of the rocker with a notch.
When centrifugally loaded, the springs in one-way clutches and brakes compress against the rockers. This increases stress on the spring, and increases the chance that the spring will be expelled from the pocket.
Conventional one-way brakes and clutches develop relatively large magnitudes of hoop stress in the races when torque is transmitted through the brake; therefore, the races of conventional one-way brakes are formed of bearing grade steel in order to withstand the operating hoop stress. Clutches formed of powdered metal potentially can be produced at relatively low cost compared to the cost to form and produce a conventional clutch or brake of high grade steel, provided extensive machining is avoided.
The clutches described in the U.S. Pat. Nos. 5,070,978 and 5,947,245, however, require a significant amount of machining of the components that are formed of powdered metal. Excessive internal backlash, which can produce noise at unacceptable levels, is a potential problem under certain operating conditions with these clutches.
Conventionally, the actuating spring might be retained by configuring the surrounding surfaces at the spring recess such that operating stress in the spring is lower than the strength of the spring and that the spring would not be expelled from the pocket. But these surfaces are formed so they perform multiple functions that influence performance of the rocker. Imposing an additional spring retention requirement would compromise their ability to perform the other functions and impair design flexibility. A need exists in a one-way clutch or brake to secure the springs that actuate the rockers in a spring recess, thereby preventing inadvertent escape of the spring from the recess while in service, while being transported and during handling.